A printed circuit board is provided with holes for mounting a component as required. The leads of a component are each inserted through one of the holes, and the lead is soldered to a land around the hole. Punching a circuit board with a die is executed as a method of forming such holes.
However, since the diameter of a hole has been designed so as to be equal to the inner diameter of a land, when a circuit board is punched out with a die press in a circuit board manufacturing process, the following situation may occur: a wiring pattern formed on the substrate thereof by etching or the like after producing of a material board can peel easily to leave a burr thereon. If a burr is left thereon, the printed circuit board becomes a defective piece, thus reducing yields thereof. If a circuit board where a burr is left thereon is used as it is, the board can cause a short circuit when the burr downward falls. Further, produced printed circuit boards are stacked when they are transported, and thus a board where a burr is left can also damage another board. Technologies of preventing a burr from being left on a circuit board when holes are punched out in the board include those disclosed in the following Patent Documents 1 and 2, for instance.
Patent Document 1: JP-A-2002-052494
Patent Document 2: JP-A-1987-094296
The technology of preventing a burr from being left thereon disclosed in Patent Document 1 punches out holes in a circuit board through a sheet and requires the additional preparation of the sheet. Moreover, the technology requires that the sheet-be processed. Furthermore, the technology disclosed in Patent Document 2 punches holes by providing isolated lands on the side of a board opposite lands used in the circuit board, and requires that such isolated lands be anew provided thereon.
The present invention has been accomplished to solve such a technical situation, and an object thereof is to prevent a burr from being left on a printed circuit board when holes are punched out in the board, in a simpler structure and by a simpler method.